Cr2O3 (Chrome Oxide)

Notas

Chromium(III) oxide (Cr2O3) acts as a refractory pigment within ceramic glazes and glass systems. It is the most stable chromium oxide and occurs naturally as the mineral eskolaite. In glaze chemistry, it is characterized by its low solubility; it does not readily form silicates or integrate with fluxes. Consequently, addition levels above 1% often lead to opacification as the particles fail to dissolve in the melt. While it provides a consistent, drab green coloration across various firing atmospheres and temperatures, it becomes volatile near 1240°C, releasing toxic fumes. Chromium is highly reactive; it produces brownish tones in the presence of zinc due to the formation of zinc chromate and can cause blistering in enamel ground coats. To achieve stable pinks, it is frequently combined with tin, though this interaction requires specific glaze chemistry—typically high calcium or strontium content and an absence of zinc—to be effective, often yielding better results when introduced via a premelted commercial stain. To clarify green glazes, alumina and calcium carbonate are preferred over tin. Furthermore, the pigment can be modified; cobalt additions shift the color toward peacock green, while zircon opacifiers help prevent unwanted brown edges. As a body stain, it is effective in concentrations up to 5%.